The present invention relates to a production method of a heat pipe roller holding a heating medium therein.
In the heating rollers as employed in copying apparatus or the like, it is preferable that the temperature of the heating rollers can be elevated speedily to a predetermined temperature.
In some conventional copying apparatus a heat pipe roller containing a heating medium which is vaporized by heating, is employed to attain a speedy elevation of temperature.
FIG. 1 shows the conventional apparatus for producing a heat pipe roller. In the figure, heat pipe roller 2 having a chamber for holding a heating medium therein is made of a heat resistant metal and is formed so as to be free from any leakage of the heating medium. One end of a pipe 3 is inserted into one end plate 2a of the heat pipe roller 2, and the other end of the pipe 3 is connected to a vacuum pump 5 through a valve 4. Another pipe extends from the pipe 3, between the heat pipe roller 2 and the vacuum pump 5 and is connected to a tank 7 through a valve 6. Heating medium 8 is placed in the tank 7. When this conventional apparatus is used, the heat pipe roller 2 is produced by the following steps. The heat pipe roller 2 is heated by heater 9 so that dust and oily dirt which might adhere to the interior wall of the heat pipe roller 2 are removed by combustion, and at the same time, the heat pipe roller 2 is evacuated with the vacuum pump 5.
When the heat pipe roller 2 has cooled, the heating medium is loaded into the heat pipe roller 2. Since the pressure in the heat pipe roller 2 is lowered while the heat pipe roller cools, the pressure (or the vacuum level) in the roller has to be readjusted to a predetermined pressure by the vacuum pump 5, and then the heat pipe roller is sealed.
In this conventional method, the whole apparatus has to be designed so as to be made airtight and free from any leakage of the heating medium, particularly when the heating medium is loaded into the heat pipe roller. This results in that the apparatus has a shortcoming of being rather expensive and involving the above-mentioned complicated steps.
Alternatively, there is a method in which air in the heat pipe roller is replaced by an inert gas, such as helium, after the heating medium has been loaded into the heat pipe. The inert gas is then sucked from the chamber by the vacuum pump in order to obtain a predetermined vacuum level in the heat pipe. This method as well has the same shortcoming as in the above-mentioned method.